Velocity modulation amplifier tube



June 9, 1953 E. TOURATON ETAL 2,641,730

VELOCITY MODULATION AMPLIFIER TUBE Filed Oct. 7, 1947 IN VEN TORS 5/ 1/1142 mu/mrwv HNDAE P/QUET cz nun: owwawsfnu Patented June 9, '1953 Emile Touraton,v AndrPiquet, and Claude Dir-- mousseau, Paris,, France, assignors' to International Standard Electric. Corporation, New York, N. Y., a corporation. of Delaware Application October 7, 1941;..SeziaINo; 77836L In France August 21, 194'6 Section 1, Public Law 691), August 8,1946

Patent expires August 21', 1966 1 Claim.

The-present invention relates to improvements in speed modulation amplifier tubes and, more particularly, to improvements invelocity modulation 'amp'l'ifier tube capablef wide frequency pass bands. I Velocity modulation tubes inwhich-the resonant volumes are replaced by waveguides have been proposed; In these tubes, the output power isdependent on the length, and this presents certain drawbacks from the viewpoint of size.

One of the objects of the present invention relates-to wide pass band speed modulation amplifier tubes that occupy small space.

Another object of the present invention relates to speed" modulation amplifier tubes that furnish a considerableg-a in from low input levels. According to one ofthe features of the present invention, a speed modulation amplifier 1 tube comprises a vacuum envelope, a circular electron gun, a wave guide folded in spiral form, and a target electrode that collects the electrons emitted by theelectron gun. I I

According to another feature of the present invention, the Wave guide folded in spiral form is excited at one of its ends by the signal to beamplified, and the available energy is tapped at its other end. One or more openings are provi'ded along the Wave guide so as to permit passage of the electron beam with a suitable transit time. The spiral has such a pitch that the electrons takethe same .time to pass from one spire to another as the. wave to be amplified does to pass, over the same spire. I

According to another feature of the present invention, a. speed modulation amplifier tube comprises a wave guide folded in fretwork form and an electron gun-that'produces a narrow electron beam.

According. to another feature of the present invention, a speed modulation amplifier tube comprises meansthatmake it possible to produce an axial magnetic field in orderto facilitate the concentration of the electron beam.

Other objects, features and advantagesof the present invention will be found upon reading the following description given with reference to the appended drawings, which are without limitation and in which:

Fig. 1 shows diagrammatically an example of embodiment of a wide pass band velocity modulation amplifier tube incorporating features of the present invention.

Fig. 2 is a plan view of the wave guide of Fig. 1.

Fig. 3 is a fragmentary view showing section through thewave guide of the example" of embodiment of Fig. 1.

"Fig: 4' shows sectional view of an example of embodiment of a circular electron gun.

Fig. 5' is a schematic of the developed image of the spires'of the wave guide.

Fig. 6 shows an example of embodiment of the concentration of the electron beam by a magnetic field produced by" a solenoid.

Fig. '7 shows another: example of embodiment of a wide pass. band speed modulation. tube employing features of the present invention.

Referring to Figs..1 and 2, these show an example of embodiment of a wide pass band speed modulation tube incorporating features of the present invention.

A v-acuumtenvelope lencloses the various 'elec- I trodes, particularly an electron gun 2, a wave guide folded in spiral .form 3, and a target 4 which collects the electrons that issue from electron gun 2 after their passage through the spires off;g:uide-- -3; The electrodes are supported in envelope l' byv supports 5- sealed to the walls of the envelope, or in any other known manner.

The outlet-terminals of electron gun 2 and of target 4 are not shown in the drawings. The waveguide: passes: through the hermetically sealed vacuum envelope I, and its ends are. extended outwardly as shown in thedrawing.

Fig. 3 shows a section of the waveguide of Fig.

1. The arrows indicate the path of the electron beam that passes over all or part of the guides periphery. For this purpose, there is provided an electron gun of the annular type, e. g.'like the one shown in Fig. 4. A ring-shaped cathodefi iswdisposed within a focusing electrode 1, and it servesfor forming an annular electron beam and guiding it to the outlet of cathode B:

The electron beam that issues from electron' gun 2 passes over all the spires of wave guide 3. As'shown by the-arrows in Fig. l, the amplifier is excited on the left hand side and the available energy is" collected on the right-hand side at the outlet of the: guide.

Taking two successive spires of wave guide 3-, the tube "operates'like' the amplifier described in the abovementioned patent application. It can accordingly be seen that the tube assembly may be likened to a certain number of elementary amplifiers in cascade, each of these elementary amplifiers consisting of two spires. In order that the energies of these elementary amplifiers may be additive and in phase, the pitch of the spiral of wave guide 3 has to be such that the electrons take the same time in passing from one spire to another as the wave to be amplified does in passing over the spire. The electron grouping thus takes place at each passage from one spire of the spiral'to another. 7

The pass band of the amplifier made up in this way is theoretically infinite above the inond spire will be KEL, L being the length of a spire. To this voltage is added the voltage E of the first spire, making a total:

E2=KEL+E=E'(KL+1) V If.KL 1, 1 may be-neglected as regards KL, and

E2=KL.E.

At a point X of the third spire, the developed voltage will be Taking G to be the gain from the first to the second spire, the total gain will be:

Gun-1) This shows that the gain obtained maybe'co'nsiderable with a relatively small number of spires of the wave guide. 1 i

In order to prevent transverse dispersion of the electron sheet, means are provided for producing a uniform magnetic field parallel to the beam. It is possible, for example, to obtain this magnetic field by means of a solenoid having the same axis as the tube and traversed by a direct current of suitable value, as shown in Fig; 6. I

An example of embodiment ofa wide pass band speed modulation tube of medium power is shown in Fig. 7.

A vacuum envelope I2 encloses an electron gun comprising a cathode I3, e. g. of thecircular type, and a focusing electrode M within which cathode i3 is located. A wave guide I5 is disposed along the tube and is folded in fretwork form, the wave to be amplified arriving on the left-hand side and'the available energy being tapped on the right hand side, as shown by the arrows. A target it collects the electrons that issue from the electron gun after their passage through'the horizontal portions of wave guide I5.

the Wave 4 As explained above, the gain increases along the tube. There is no constant accompaniment by the electronbeam, as described. in the previous Suitable phase conditions have to be examples. respected in order to make additive the voltages developed in each elementary unit, and this determines the distance 3/ between. two consecutive horizontal portions.

The electron beam has however to be relatively narrow, and the available power is consequently limited.

' .As before, focusing means may be. provided in order to guide the electron beam along the tube.

Although the present invention has been described for certain examples of embodiment, it

is evident that it is by no means limited thereto, but that the same are capable of numerous variants and modifications without departing from the scope of the invention.

The described amplifiertubes have the. advantage of small size owing to the special arrangement of their members, and they are capable of important gains from low input levels.

What is claimed is: An amplifier of the velocity modulated type comprising a tubular envelope, an annular cathode within saidenvelope, an annular focussing electrode adjacent said cathode forming an electron gun therewith for producing an annular electron beam, at target electrode in the path of said electron beam, and a helical wave guide positioned between said electron gun and said adjacent said cathode, and for the collection of the applied waves at the end adjacent said target electrode, said waveguide helix having a pitch such that electrons of said beam take substantially the same time passingfrom one turn to the next adjacent turn as said Waves to be amplified in passing around a single turn.

' EMILETOURATON.

ANDRE PIQUET. CLAUDE DUMOUSSEAU.

' References Cited in theme of this patent UNITED STATES PATENTS Number Name Date 2,064,469 I-Iaeff Dec. 15, 1936 2,300,052 vLindenblad Oct. 27, 1942 2,367,295 Llewellyn Jan. 16, 1945 2,368,031 Llewellyn -Jan. 23, 1945 2,541,843 Tiley July 18, 1947 2,575,383

Field NOV. 20, 1951 

